OVERSPEED SAFETY DEVICES

Mechanical overspeed trips depend on the cen-trifugal forces developed by the engine and should be maintained in good working condition. A faulty overspeed device can endanger not only the engine but also personnel if the engine explodes or flies apart because of uncontrolled speed. The engine instruction manual contains infor-mation as to the speed at which the overspeed is supposed to function. Most overspeed trips are adjustable. Prior to making any change in the ad-justment of the overspeed trip, determine if the engine did not trip out for some reason other than the action of the element of the overspeed trip. It is highly advisable that you first check the ac-curacy of the tachometer and then test the overspeed trip. All spring tension adjustments and linkage adjustments to an overspeed trip are critical. Instructions given for making these ad-justments are found in the manufacturer’s instruc-tions

manual and must be followed. Hydraulic overspeed trips are extremely sen-sitive to dirt. Dirt or lacquer-like deposits may cause a trip to bind internally. The speed sensitive element must be kept clean and so should all parts of the linkage and mechanisms incorporated in this speed sensitive element. When painting around the engine, the painter should be cau-tioned against allowing paint to fall on joints, springs, pins, and other critical points in the linkage.

All linkage binding should be eliminated. If parts are bent, badly worn, improperly installed, dirty, or if their motion is restricted by some other part of the engine, the trip will not function properly. On occasion the drive shaft of the overspeed trip may be broken and prevent rota-tion of the flyweight and the overspeed trip. Insufficient oil in the hydraulic trip may be another source of this problem. Oil should be maintained at the level specified in the instruc-tion manual.

The cause of any malfunction should be deter-mined and eliminated. This will involve cleaning the trip and its linkage, removing the source of binding, replacing faulty parts, adding oil to hydraulic type trips, or adjusting the speed sen-sitive element, always in accordance with the in-struction manual. If the trip has been damaged, it is advisable to install a spare overspeed trip and completely rebuild or overhaul the damaged one.

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